Many industries use pulverized coal as the main source of fuel in their furnaces and/or boilers. Additionally, the steel industry supplies pulverized coal to its blast furnaces in an effort to both reduce the amount of coke that normally would be consumed there and to replace other combustible fuels which might otherwise be used as its heat source.
Generally, such pulverized coal is supplied to the furnace or boiler via a pneumatic injection system. Additionally, in the steel industry, it is common for such a pneumatic injection system to incorporate a mixture of both air and nitrogen as the conveying medium. Thus, this gaseous air/nitrogen mixture is used to convey the coal to each blast furnace tuyere or nozzle so it can be burned with the furnace hot blast.
Unfortunately, however, it has been found that during such operation, deposits of fine coal built up on the inside surface of these pulverized coal delivery lines and also on the inside surface of related equipment such as tubing, nozzles, reservoirs, and the like. It has also been found that when certain coals were used, this internal buildup increased dramatically thereby severely reducing the ability to deliver pulverized coal to the furnace.
In the past, attempts to rectify this problem have included the specification of the use of only certain coals which exhibit a low deposition rate. However, over time, deposits may still occur. Other attempts have included frequent air/nitrogen purging of the system or the use of shot cleaning with steel balls or other materials to dislodge the deposits. A more extreme solution involves the disassembly of the system and the manual cleaning of its various components. Because the cleaning methods noted are only temporarily effective, they must be repeated frequently. Each such cleaning cycle interrupts operations thereby further increasing their overall cost to the industry. On the other hand, by electing to continue to operate with a partially clogged delivery system, power requirements will increase and system capacity may be reduced which results in a significant economic penalty.
Another problem faced by steel producers is the need to dispose of significant quantities of an operational by-product referred to as coke breeze. Coke breeze is a granular, carbon based substance that is generated in the coke production and handling process. This material is unsuitable for charging into the blast furnaces of steel mills because of its small particle size. One of the largest uses for coke breeze has been in iron ore sintering plants where the coke breeze is mixed with the iron ore and other constituents as a source of energy for the sintering process. However, because these same sintering plants have been the source of significant particulate and gaseous emissions, many of them have closed or are now shutdown. Consequently, the demand for coke breeze for use in sintering plants has diminished, thereby causing excess coke breeze to become a disposal problem.
It is thus an object of the present invention to provide an economical means of cleaning pulverized coal delivery lines. Another object of the present invention is to provide a means of either continuously cleaning such lines or intermittently cleaning them, as desired. Yet another object of the present invention is to provide a means of cleaning a pulverized coal injection system without any interruption of the ongoing operations. A further object of this invention is to provide a means of cleaning whose effectiveness can be monitored through variations in injecting pressure requirements. Still another object of the present invention is to clean such lines through abrasion using granular coke breeze. Yet another object of this invention is to equip facilities utilizing a pulverized coal injection system with a means of disposing of excess coke breeze. A further object of this invention is to dispose of the excess coke breeze by burning it thereby also making use of its high carbon content. These and other objects and advantages will become obvious upon further investigation.